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EAS 100 Global atmospheric circulation

EAS 100 Global atmospheric circulation. Key points • global distribution of solar energy • buoyancy of air • convection • convergence and divergence • Hadley circulation • Coriolis effect • Intertropical Convergence Zone • westerlies and trades • subtropical highs.

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EAS 100 Global atmospheric circulation

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  1. EAS 100 Global atmospheric circulation Key points • global distribution of solar energy • buoyancy of air • convection • convergence and divergence • Hadley circulation • Coriolis effect • Intertropical Convergence Zone • westerlies and trades • subtropical highs

  2. • Incoming solar energy flux (W/m2) decreases with latitude

  3. • Energy is continuously redistributed from regions of surplus energy to ones of net deficit; this is the origin of atmospheric circulation

  4. • Heated air tends to rise (buoyancy), since volume (and hence density) are related to temperature PV=nRT (Ideal gas Law) • Greatest heating occurs in the tropics, leading to rising air masses • The decreased mass of this air results in low atmospheric pressure • Air flows from zones of high to low pressure

  5. Hadley circulation: convective cells ultimately fuelled by the excess solar energy received in the tropics (InterTropical Convergence Zone - ITCZ)

  6. Idealized view What’s missing?

  7. The Earth rotates Where drag and friction are minimal, and over large distances, the Earth’s rotation imparts a deviation from linear trajectories of movement: the Coriolis effect

  8. Putting it all together

  9. North America ITCZ Subtropical highs Westerlies and subpolar low

  10. Africa Subtropical highs ITCZ Subtropical highs Westerlies and subpolar low

  11. A final consideration: seasonal migration of the ITCZ due to the tilt of the Earth’s axis (23.5˚ from vertical)

  12. The ITCZ migrates 10-20˚ north and south of the Equator on a seasonal basis, closely reflecting the zone of maximum solar energy receipt, and dictating important weather phenomena (monsoons, etc.)

  13. SUMMARY • The driving force of atmospheric circulation is the global distribution of solar energy • Due to the incident angle of incoming solar radiation, there is more solar energy in the tropics, resulting in an equator-to-pole temperature gradient • High temperatures produce buoyant air and hence low pressure • Air flows from high to low pressure, resulting in winds • Winds are subjected to the Coriolis effect from Earth’s rotation • Global circulation redistributes available thermal energy from hot to cold areas, thus providing a negative feedback against runaway heating of the tropics, and cooling of the poles

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